Control method for an AC-DC conversion circuit

ABSTRACT

The present disclosure provides a control method for an AC-DC conversion circuit. The method includes: in an entire load range, acquiring circuit parameter information of the AC-DC conversion circuit; limiting an actual switching frequency or an actual switching period of the AC-DC conversion circuit within a preset working range according to the circuit parameter information. The AC-DC conversion circuit can meet requirements of Total Harmonic Distortion (THD), Power Factor (PF), efficiency and Electromagnetic Interference (EMI) and the like by adjusting the working information of the AC-DC conversion circuit through the preset working range.

CROSS-REFERENCE TO RELATED APPLICATION

This application a continuation application of U.S. patent applicationSer. No. 17/199,472, filed on Mar. 12, 2021, which claims priority toChinese Patent Application No. 202010217069.5, filed on Mar. 25, 2020.Both of the two applications are hereby incorporated by reference intheir entireties.

TECHNICAL FIELD

The present disclosure relates to the technical field of power supply,and in particular, to a control method for power supply.

BACKGROUND

Recently, miniaturization and high power density have become thedevelopment trend of Switching Mode Power Supply (SMPS). In order toimprove the switching frequency and the power density of the SMPS, thealternating current to direct current (AC-DC) conversion circuit isoften controlled to work in critical conduction mode (CRM), because theAC-DC conversion circuit has no reverse recovery loss in the CRM.However, the switching frequency largely varies in the CRM, and limitedto the driving ability of the driver chip and the loss of circuitcomponents and magnetic parts, the switching frequency of the circuitneeds to be limited to a certain range. So controlling the AC-DCconversion circuit to work in the single CRM could not meet therequirements of Total Harmonic Distortion (THD), Power Factor (PF),efficiency, and Electromagnetic Interference (EMI) characteristics atthe same time.

SUMMARY

The present disclosure provides a control method for an AC-DC conversioncircuit, and implements different working modes according to differentinput voltages and different loads, so as to improve the aspects ofperformance, such as THD, PF, efficiency, EMI of the AC-DC conversioncircuit.

The present disclosure provides a control method, including: acquiringcircuit parameter information of an AC-DC conversion circuit; andlimiting an actual switching frequency or an actual switching period ofthe AC-DC conversion circuit in an entire load range to a preset workingrange according to the circuit parameter information.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in embodiments of the presentdisclosure or in the prior art more clearly, the following brieflyintroduces the accompanying drawings needed for describing theembodiments or the prior art. Apparently, the accompanying drawings inthe following description illustrate merely some embodiments of thepresent disclosure, and persons of ordinary skill in the art may stillderive other drawings from these accompanying drawings without creativeeffort.

FIGS. 1A-1D are schematic structural diagrams of an AC-DC conversioncircuit according to an embodiment of the present disclosure;

FIG. 2 is a schematic flowchart of a control method for an AC-DCconversion circuit according to an embodiment of the present disclosure;

FIGS. 3A-3B are schematic diagrams of a control method for an AC-DCconversion circuit according to a first embodiment of the presentdisclosure;

FIG. 4 is a schematic waveform diagram of an inductor current in anAC-DC conversion circuit in different modes according to the embodiment;

FIGS. 5A-5B are schematic diagrams of a control method for an AC-DCconversion circuit according to a second embodiment of the presentdisclosure;

FIGS. 6A-6B are schematic diagrams of a control method for an AC-DCconversion circuit according to a third embodiment of the presentdisclosure;

FIG. 7 is a schematic diagram of a control method for an AC-DCconversion circuit according to a fourth embodiment of the presentdisclosure;

FIG. 8 is a schematic diagram of a control method for an AC-DCconversion circuit according to a fifth embodiment of the presentdisclosure;

FIG. 9 is a schematic diagram of a control method for an AC-DCconversion circuit according to a sixth embodiment of the presentdisclosure;

FIG. 10 is a schematic diagram of a control method for an AC-DCconversion circuit according to a seventh embodiment of the presentdisclosure;

FIG. 11 is a schematic diagram of a control method for an AC-DCconversion circuit according to an eighth embodiment of the presentdisclosure;

FIG. 12 is a schematic diagram of a combination of working modesaccording to an embodiment of the present disclosure;

FIGS. 13A-13B are schematic diagrams of a control method for an AC-DCconversion circuit according to a ninth embodiment of the presentdisclosure;

FIGS. 14A-14B are schematic diagrams of a control method for an AC-DCconversion circuit according to a tenth embodiment of the presentdisclosure;

FIGS. 15A-15B are schematic diagrams of a control method for an AC-DCconversion circuit according to an eleventh embodiment of the presentdisclosure;

FIG. 16 is a schematic structural diagram of a control apparatus for theAC-DC conversion circuit according to embodiments of the presentdisclosure;

FIG. 17 is a schematic structural diagram of another control apparatusfor the AC-DC conversion circuit according to embodiments of the presentdisclosure; and

FIG. 18 is a schematic diagram of a hardware structure of an electronicdevice according to an embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

To make the objectives, technical solutions, and advantages ofembodiments of the present disclosure clearer, the following clearly andcomprehensively describes the technical solutions in the embodiments ofthe present disclosure with reference to the accompanying drawings inthe embodiments of the present disclosure. Apparently, the describedembodiments are merely a part rather than all embodiments of the presentdisclosure. All other embodiments obtained by persons of ordinary skillin the art based on the embodiments of the present disclosure withoutcreative effort shall fall within the protection scope of the presentdisclosure.

The terms “including” and “comprising” and any variations thereof asused herein are intended to cover non-exclusive inclusions, for example,processes, methods, systems, products or devices that contain a seriesof steps or units are not limited to the steps or units clearly listed,but may include other steps or units that are not explicitly listed orare inherent in these processes, methods, products, or devices.

The “an embodiment” or “another embodiment” mentioned throughout thespecification of the present disclosure means that a specific feature,structure, or characteristic related to the embodiment is included in atleast one embodiment of the present disclosure. Therefore, “in anembodiment” or “in the embodiment” appearing throughout thespecification does not necessarily refer to the same embodiment. Itshould be noted that the embodiments and the features therein in thescheme can be combined with each other without conflict.

In order to solve the problem in the prior art that controlling theAC-DC conversion circuit to work in a single CRM could not meet therequirements of Total Harmonic Distortion (THD), Power Factor (PF),efficiency and Electromagnetic Interference (EMI) at the same time, thepresent disclosure provides a control method for the AC-DC conversioncircuit, which may implement different working modes according todifferent input voltages and different loads, so as to improve theaspects of performance, such as THD, PF, efficiency, EMI of the PFCcircuit. The implementation processes of the present disclosure arespecifically described below with reference to several embodiments.

The execution subject of the present disclosure is an electronic device,which includes an AC-DC conversion circuit and a control apparatusconnected to the AC-DC conversion circuit. The topology of the AC-DCconversion circuit can be a bridgeless PFC topology as shown in FIGS.1A-1B. As shown in FIG. 1A, a first bridge arm includes two powerswitches S1 and S2, and a second bridge arm includes two diodes D1, D2,a midpoint of the first bridge arm is connected to a power grid throughan inductor L1, and a midpoint of the second bridge arm is connected tothe power grid through an inductor L2. As shown in FIG. 1B, a firstbridge arm includes two power switches S1, S2, and a second bridge armincludes two power switches S3 and S4, a midpoint of the first bridgearm is connected to the power grid through the inductor L1, and amidpoint of the second bridge arm is connected to the power grid throughan inductor L2. In the above embodiments, the bridgeless PFC has twoinductors L1 and L2. In some other embodiments, the bridgeless PFC mayonly have one inductor as shown in FIGS. 1C-1D, which is not limited inthe present disclosure. Further, the control apparatus controls thepower switches S1 and S2 in the AC-DC conversion circuit shown in FIG.1A, or controls the power switches S1-S4 in the AC-DC conversion circuitshown in FIG. 1B. In some other embodiments, the AC-DC conversioncircuit may also adopt other topologies, which is not limited in thepresent disclosure.

The electronic device of the present disclosure may be applied to apower supply device in the electrical appliance or the terminal device.The present disclosure provides a control method for the AC-DCconversion circuit, by calculating working information of an AC-DCconversion circuit according to the input information and the outputinformation of the AC-DC conversion circuit, and comparing the workinginformation of the AC-DC conversion circuit with a preset working range,to obtain an actual working information of the AC-DC conversion circuit.Wherein, the input information includes an input voltage and an inputcurrent, the output information includes an output voltage and an outputcurrent, and the working information includes a switching frequency or aswitching period. Through the preset working range, the workinginformation of the AC-DC conversion circuit can be adjusted to meet therequirements of Total Harmonic Distortion (THD), Power Factor (PF),efficiency and Electromagnetic Interference (EMI) and the like.

FIG. 2 is a schematic flowchart of a control method for the AC-DCconversion circuit according to an embodiment of the present disclosure.Referring to FIG. 2 , the method includes:

S101: calculating a switching frequency of the AC-DC conversion circuitaccording to at least one circuit parameter information of an inputvoltage, an input current, an output voltage and an output current ofthe AC-DC conversion circuit.

Since the switching frequency is reciprocal with the switching period,the switching period of the AC-DC conversion circuit may also becalculated according to at least one circuit parameter information of aninput voltage, an input current, an output voltage and an output currentof the AC-DC conversion circuit.

It should be understood that in the present disclosure, one or acombination of any two or more of multiple parameters such as the inputvoltage, the input current, the output voltage and the output current ofthe AC-DC conversion circuit can be used to calculate the switchingfrequency of the AC-DC conversion circuit.

In some embodiments, the switching frequency can be calculated by thefollowing formula:

${F( {V_{in},I_{in},V_{o},I_{o}} )} = \frac{V_{in}( {V_{o} - {\sqrt{2}V_{in}{❘{\sin( {2\pi ft} )}❘}}} )}{2I_{in}I_{o}{LV}_{o}^{2}}$

Wherein, Vin is the input voltage, Iin is the input current, Vo is theoutput voltage, Io is the output current, and L is inductance value ofthe inductor. It should be noted that the calculation of the switchingfrequency is not limited to this.

S102: comparing the switching frequency of the AC-DC conversion circuitwith a preset switching frequency range to obtain an actual switchingfrequency and a working mode of the AC-DC conversion circuit.

For example, the calculated switching frequency of the AC-DC conversioncircuit is compared with the preset switching frequency range to obtainthe actual switching frequency of the AC-DC conversion circuit; or thecalculated switching period of the AC-DC conversion circuit is comparedwith a preset switching period range to obtain the actual switchingperiod of the AC-DC conversion circuit.

Wherein, an upper limit and a lower limit of a preset working range inthe embodiment may be preset fixed values, or both may be variablevalues that vary with a variable, such as the input voltage or a workingtime or a working phase. Specifically, an upper limit and a lower limitof the switching frequency range may be preset fixed values, or both maybe variable values that vary with a variable, such as the input voltageor the working time or the working phase. Correspondingly, an upperlimit and a lower limit of the switching period range may be presetfixed values, or both may be variable values that vary with a variable,such as the input voltage or the working time or the working phase.

Further, in some embodiments, the control method includes: comparing theworking information of the AC-DC conversion circuit with the presetworking range, so as to determine the working mode of the AC-DCconversion circuit, and drive the AC-DC conversion circuit to work inthe corresponding working mode.

Exemplarily, the working mode includes one or more of the following:Continuous Conduction Mode (CCM), Critical Conduction Mode (CRM) andDiscontinuous Conduction Mode (DCM).

If the switching frequency is greater than or equal to a maximumfrequency threshold, the working mode of the AC-DC conversion circuit iscontrolled to be DCM or CCM, and the actual switching frequency of theAC-DC conversion circuit is controlled to be the maximum frequencythreshold, wherein the maximum frequency threshold is the upper limit ofthe preset switching frequency range. Wherein, in a condition that theDCM is selected while the switching frequency is greater than or equalto the maximum frequency threshold, a better PF is obtained by changinga charging time, meanwhile, a driving loss is reduced by limiting themaximum frequency, which is convenient for the selection of circuitcomponents and magnetic parts. In a condition that the CCM is selectedwhile the switching frequency is greater than or equal to the maximumfrequency threshold, a ZVS can be realized, thereby reducing switchingloss, meanwhile, the driving loss is reduced by limiting the maximumfrequency, which is convenient for the selection of circuit componentsand magnetic parts.

FIGS. 3A-3B are schematic diagrams of a control method for the AC-DCconversion circuit according to a first embodiment of the presentdisclosure. Referring to FIGS. 3A-3B, the switching frequency F(Vin,Iin, Vo, Io) is calculated according to input voltage Vin, the inputcurrent Iin, the output voltage Vo and the output current Io, and F(Vin,Iin, Vo, Io) is compared with the preset switching frequency range.During time periods T0-T1 and T6-T7, the switching frequency F(Vin, Iin,Vo, Io) is greater than or equal to the maximum frequency thresholdFmax, then the working mode of the AC-DC conversion circuit iscontrolled to the DCM, as shown in FIG. 3A and FIG. 4 ; or the workingmode of the bridgeless PFC circuit is controlled to be the CCM, as shownin FIG. 3B and FIG. 4 . And the actual switching frequency Factual isequal to the maximum frequency threshold Fmax during the time periodsT0-T1 and T6-T7.

Limiting the actual switching frequency of the bridgeless PFC lower thanthe maximum frequency threshold can reduce the driving loss andfacilitate the selection of circuit components or magnetic parts,meanwhile, in the DCM working mode, a better PF can be obtained bychanging the charging time, and in the CCM working mode, ZVS can berealized, thereby reducing the switching loss.

If the switching frequency is less than or equal to a minimum frequencythreshold, the working mode of the AC-DC conversion circuit iscontrolled to be the CCM, and the actual switching frequency of theAC-DC conversion circuit is controlled to be the minimum frequencythreshold, wherein the minimum frequency threshold is the lower limit ofthe preset switching frequency range.

For example, as shown in FIGS. 3A-3B, during the time period T3-T4, theswitching frequency F(Vin, Iin, Vo, Io) is less than or equal to theminimum frequency threshold Fmin, then the working mode of thebridgeless PFC circuit is controlled to be the CCM, so that theswitching frequency Factual is equal to the minimum frequency thresholdFmin during the time period T3-T4.

In the CCM working mode, by selecting different switching frequencies,the actual switching frequency of the bridgeless PFC is limited to benot less than the minimum frequency threshold, which can reduce acurrent ripple, improve efficiency, and facilitate EMI design.

It should be noted that the CCM with the switching frequency being lessthan or equal to the minimum frequency threshold Fmin is different fromthe CCM with the switching frequency being greater than or equal to themaximum frequency threshold Fmax, as shown in FIG. 4 . A current of theCCM adopted in a condition that the switching frequency F(Vin, Iin, Vo,Io) is less than or equal to the minimum frequency threshold Fmin iscontinuous, and a current of the CCM adopted in a condition that theswitching frequency F(Vin, Iin, Vo, Io) is greater than or equal to themaximum frequency threshold Fmax is continuous and there is a negativecurrent.

If the switching frequency is less than the maximum frequency thresholdbut greater than the minimum frequency threshold, the working mode ofthe AC-DC conversion circuit is controlled to be the CRM. For example,as shown in FIGS. 3A-3B, during time periods T1-T3 and T4-T6, in acondition that the switching frequency F(Vin, Iin, Vo, Io) is betweenthe minimum frequency threshold Fmin and the maximum frequency thresholdFmax, the working mode of the bridgeless PFC circuit is controlled to bethe CRM, so that the actual switching frequency Factual is equal to thecalculated switching frequency F(Vin, Iin, Vo, Io) during the timeperiods T1-T3 and T4-T6.

In some embodiment, if the AC-DC conversion circuit works in the CRM,the present disclosure further determines a control mode of the AC-DCconversion circuit, for example Variable On-time Critical ConductionMode (VOT CRM) and Negative Current Critical Conduction Mode (NCR CRM).Wherein, the Negative Current Critical Conduction Mode is similar to aTriangular Conduction Mode (TCM), that is, the current will be negativeon the basis of the Critical Conduction Mode.

Furthermore, in some embodiments, the control method in CRM may includethe following three different implementations:

First Embodiment

Determining the control logic according to an absolute value of theinput voltage and a first voltage threshold Vth1; when the absolutevalue of the input voltage is less than or equal to the first voltagethreshold, controlling the AC-DC conversion circuit to work in the VOTCRM to change the charging time of the inductor in the AC-DC conversioncircuit; when the absolute value of the input voltage is greater thanthe first voltage threshold, controlling the AC-DC conversion circuit towork in the NCR CRM, to control the inductor current to reach a negativevalue to realize zero voltage switching ZVS of power switches.

As shown in FIGS. 3A, 3B and 4 , during time periods of T1-T2 and T5-T6,the absolute value of the input voltage Vin is less than or equal to thefirst voltage threshold Vth1, and then the working mode of the AC-DCconversion circuit is controlled to be the VOT CRM. By changing thecharging time of the inductor in the AC-DC conversion circuit, the THDof the input current when the input voltage Vin cross zero is improved,which avoids the problem of high input current THD caused by the averageinput current being zero when the AC-DC conversion circuit works in theTCM or the CRM near the zero-crossing point of the input voltage.

As shown in FIGS. 3A, 3B and 4 , during time periods T2-T3 and T4-T5,the absolute value of the input voltage Vin is greater than the firstvoltage threshold Vth1, and then the working mode of the AC-DCconversion circuit is controlled to be the NCR CRM, and the inductorcurrent in the AC-DC conversion circuit is controlled to reach anegative value to realize the ZVS of the power switches, therebyreducing the switching loss.

Second Embodiment

Determining the control logic according to a working time and a firsttime threshold Tth1. Within half a power frequency period, the switchingfrequency range Fmin and Fmax, and the actual switching frequency aresymmetrical with the time Tc as the axis, that is, the latter quarterperiod is symmetrical with the former quarter period, which isspecifically shown in FIG. 5A or 5B.

When the working time is less than or equal to the first time thresholdTth1, the AC-DC conversion circuit is controlled to work in the VOT CRM,and the charging time of the inductor in the AC-DC conversion circuitcan be changed. When the working time is greater than the first timethreshold Tth1, the AC-DC conversion circuit is controlled to work inthe NCR CRM, and the inductor current to can reach a negative value torealize the ZVS of the power switches.

Third Embodiment

Determining the control logic according to a working phase and a firstphase threshold Φth1. Within half a power frequency period, theswitching frequency range Fmin and Fmax, and the actual switchingfrequency are symmetrical with the time Tc as the axis, that is, thelatter quarter period is symmetrical with the former quarter period,which is specifically shown in FIG. 6A or 6B.

When the working phase is less than or equal to the first phasethreshold Φth1, the AC-DC conversion circuit is controlled to work inthe VOT CRM, and the charging time of the inductor in the AC-DCconversion circuit can be changed. When the working phase is greaterthan the first phase threshold Φth1, the AC-DC conversion circuit iscontrolled to work in the NCR CRM, and the inductor current can reach anegative value to realize the ZVS of the power switches.

The implementation principles and technical effects of second embodimentand third embodiment are similar to first embodiment, and will not berepeated here. The first time threshold Tth1 and the first phasethreshold Φth1 may be directly set according to the theoreticalsituation, or may be set by perform an operation such as phase lockingaccording to sampled input voltage or input current, which is notlimited in the present disclosure.

In the present disclosure, the working information of the AC-DCconversion circuit can also be the switching period. Therefore, thecontrol method may include:

Comparing the switching period of the AC-DC conversion circuit with thepreset switching period range to obtain the actual switching period ofthe AC-DC conversion circuit.

In a condition that the switching period is less than or equal to aminimum period threshold Tmin, controlling the AC-DC conversion circuitto work in the DCM or the CCM, and controlling the actual switchingperiod of the AC-DC conversion circuit to be the minimum periodthreshold Tmin, wherein the minimum period threshold is the lower limitof the preset switching period range. The AC-DC conversion circuit maywork in the DCM, which has the advantages of low driving loss and highPF, meanwhile, a maximum switching frequency of the bridgeless PFC islimited by limiting a minimum switching period thereof, which isconvenient for the selection of circuit components and magnetic parts.The bridgeless PFC may work in the CCM, the ZVS can be realized, therebyreducing the switching loss, meanwhile, the driving loss is reduced bylimiting the maximum frequency, which is convenient for the selection ofcircuit components and magnetic parts.

In a condition that the switching period is greater than or equal to amaximum period threshold Tmax, controlling the AC-DC conversion circuitto work in the CCM, and controlling the actual switching period of theAC-DC conversion circuit to be the maximum period threshold Tmax,wherein the maximum period threshold is the upper limit of the presetswitching period range. The AC-DC conversion circuit works in the CCM,which has the advantages of small current ripple, high efficiency, goodTHD and EMI.

In a condition that the switching period is less than the maximum periodthreshold but greater than the minimum period threshold, controlling theAC-DC conversion circuit works in the CRM. The AC-DC conversion circuitworks in the CRM, which can realize ZVS by a negative current to reducethe switching loss, or improve the THD of the input current when theinput voltage crossing zero by changing the charging time of theinductor.

Due to the reciprocal relationship between the switching frequency andthe switching period, the switching frequency is greater than or equalto the maximum frequency threshold F≥F_(max), so it can be deduced that

${\frac{1}{F} \leq \frac{1}{F_{\max}}},$that is the switching period is less than or equal to the minimum periodthreshold T≤T_(min), and the minimum period threshold Tmin is equal to areciprocal of the maximum frequency threshold Fmax. Correspondingly, theswitching frequency is less than or equal to the minimum frequencythreshold F≤F_(min), so it can be deduced that

${\frac{1}{F} \geq \frac{1}{F_{\min}}},$that is the switching period is greater than or equal to the maximumperiod threshold T≥T_(max), and the maximum period threshold Tmax isequal to the reciprocal of the minimum frequency threshold Fmin.Therefore, the control method according to the switching frequency inthe present disclosure may derive that the control method according tothe switching period, the control method according to the period, andthe control method according to the frequency correspond to each other,which may not be further described here, and they all belong to theprotection scope of the present disclosure.

In some embodiments, in a condition that the switching frequency isgreater than or equal to the maximum frequency threshold, in addition tocontrol the AC-DC conversion circuit to work in the DCM or the CCM, theAC-DC conversion circuit can also be controlled to work in the VOT CRM,and then it may not be necessary to fix the switching frequency to themaximum frequency threshold. In practice, the AC-DC conversion circuitmay be controlled by calculating a turn-on time according to at leastone of the input voltage, the output voltage and other information.

Taking the switching frequency as an example, in the present disclosure,the upper limit of the switching frequency range is the maximumfrequency threshold, and the lower limit of the switching frequencyrange is the minimum frequency threshold, which may be fixed values, orboth may be variable values that vary with the input voltage or theworking time or the working phase. Exemplarily, the maximum frequencythreshold and the minimum frequency threshold are corrected according toat least one variable of the absolute value of the input voltage, theworking time and the working phase of the AC-DC converter circuit, whichincludes but not limited to the following three specificimplementations.

From first aspect, the maximum frequency threshold and the minimumfrequency threshold are corrected according to the absolute value of theinput voltage and at least one voltage correction threshold. The numberof voltage correction thresholds can be set differently according todifferent actual circuit designs and different application scenarios,which is not limited in the present disclosure.

Taking a case in which two voltage correction thresholds are set as anexample to explain the present disclosure. As shown in FIG. 3A, a firstvoltage correction threshold Vth2 and a second voltage correctionthreshold Vth3 are preset. The present disclosure corrects the maximumfrequency threshold Fmax and the minimum frequency threshold Fmin of theswitching frequency range by comparing the absolute value of the inputvoltage with the first voltage correction threshold Vth2 and the secondvoltage correction threshold Vth3, so that the switching frequency rangevaries with the absolute value of the input voltage.

During the time period that the absolute value of the input voltage Vinis less than or equal to the first voltage correction threshold Vth2(the time periods T0-T1 and T6-T7 as shown in FIG. 3A), the maximumfrequency threshold Fmax is corrected to a maximum correction thresholdFmax′, wherein the maximum correction threshold Fmax′ is less than themaximum frequency threshold Fmax. Reducing the maximum frequencythreshold can reduce the driving loss, and facilitate the selection ofcircuit components and magnetic parts at the same time.

During the time period that the absolute value of the input voltage Vinis greater than the first voltage correction threshold Vth2 (the timeperiod T1-T6 as shown in FIG. 3A), the maximum frequency threshold Fmaxis kept unchanged.

During the time period that the absolute value of the input voltage Vinis greater than or equal to the second voltage correction threshold Vth3(the time period T3-T4 as shown in the FIG. 3A), the minimum frequencythreshold Fmin is corrected to a minimum correction threshold Fmin′,wherein the minimum correction threshold Fmin′ is greater than theminimum frequency threshold Fmin. Increasing the minimum frequencythreshold can reduce the inductance current ripple, facilitate EMIdesign and improve efficiency.

During the time period that the absolute value of the input voltage Vinis less than the second voltage correction threshold Vth3 (the timeperiods T0-T3 and T4-T7 as shown in the FIG. 3A), the minimum frequencythreshold is kept unchanged.

From second aspect, the maximum frequency threshold and the minimumfrequency threshold are corrected according to the working time and atleast one time correction threshold. The number of time correctionthresholds can be set differently according to different actual circuitdesigns and different application scenarios, which is not limited in thepresent disclosure.

FIGS. 5A-5B are schematic diagrams of an AC-DC conversion circuitcontrol method according to a second embodiment of the presentdisclosure. As shown in the FIGS. 5A-5B, a first time correctionthreshold Tth2 and a second time correction threshold Tth3 are preset.The present disclosure corrects the maximum frequency threshold Fmax andthe minimum frequency threshold Fmin of the switching frequency range bycomparing the working time t with the first time correction thresholdTth2 and the second time correction threshold Tth3, so that theswitching frequency range varies with the working time.

During the time period that the working time t is less than or equal tothe first time correction threshold Tth2 (such as the time periodT0-T1), the maximum frequency threshold Fmax is corrected to the maximumcorrection threshold Fmax′, wherein the maximum correction thresholdFmax′ is less than the maximum frequency threshold Fmax. Reducing themaximum frequency threshold can reduce the driving loss, and facilitatethe selection of circuit components and magnetic parts at the same time.

During the time period that the working time t is greater than the firsttime correction threshold Tth2 (such as the time period T1-Tc), themaximum frequency threshold Fmax is kept unchanged.

During the time period that the working time is greater than or equal tothe second time correction threshold Tth3 (such as the time periodT3-Tc), the minimum frequency threshold Fmin is corrected to the minimumcorrection threshold Fmin′, wherein the minimum correction thresholdFmin′ is greater than the minimum frequency threshold Fmin. Increasingthe minimum frequency threshold can reduce the inductance currentripple, facilitate EMI design and improve efficiency.

During the time period that the working time t is less than the secondtime correction threshold Tth3 (such as the time period T0-T3), theminimum frequency threshold Fmin is kept unchanged.

Further, after the switching frequency range is corrected, the workingmode of the AC-DC conversion circuit may be determined according to themethod provided in any of the foregoing embodiments. For example, duringthe time period T0-T1, the switching frequency F is greater than Fmax′,the actual switching frequency Factual is equal to Fmax′, and the AC-DCconversion circuit may work in the DCM as shown in FIG. 5A, or the AC-DCconversion circuit may work in the CCM as shown in FIG. 5B. During thetime period T3-Tc, the switching frequency F is less than Fmin′, theactual switching frequency Factual is equal to Fmin′, and the AC-DCconversion circuit works in the CCM. During the time period T1-T3, theswitching frequency F is greater than Fmin′ but less than Fmax′, and theAC-DC conversion circuit works in the CRM. Further, the control logic ofthe circuit in the CRM is determined by comparing the working time twith the first time threshold Tth1. For example, during the time periodT1-T2, the working time t is less than the time threshold Tth1, then theAC-DC conversion circuit works in the VOT CRM; during the time periodT2-T3, the working time t is greater than the first time threshold Tth1,then the AC-DC conversion circuit works in the NCR CRM. Within half apower frequency period, the latter quarter period and the former quarterperiod are symmetrical with the time Tc as the axis, which is notrepeated here.

From third aspect, the maximum frequency threshold and the minimumfrequency threshold are corrected according to the working phase and atleast one phase correction threshold. The number of phase correctionthresholds can be set differently according to different actual circuitdesigns and different application scenarios, which is not limited in thepresent disclosure.

FIGS. 6A-6B are schematic diagrams of an AC-DC conversion circuitcontrol method according to a third embodiment of the presentdisclosure. As shown in the FIGS. 6A-6B, a first phase correctionthreshold Φth2 and a second time correction threshold Φth3 are preset,and the maximum frequency threshold Fmax and the minimum frequencythreshold Fmin of the switching frequency range are corrected bycomparing the working phase Φ with the first phase correction thresholdΦth2 and the second phase correction threshold Φth3, so that theswitching frequency range varies with the working phase.

During the time period that the working phase Φ is less than or equal tothe first phase correction threshold Φth2 (such as the time periodT0-T1), the maximum frequency threshold Fmax is corrected to the maximumcorrection threshold Fmax′, wherein the maximum correction thresholdFmax′ is less than the maximum frequency threshold Fmax. Reducing themaximum frequency threshold can reduce the driving loss, and facilitatethe selection of circuit components and magnetic parts at the same time.

During the time period that the working phase Φ is greater than thefirst phase correction threshold Φth2 (such as the time period T1-Tc),the maximum frequency threshold Fmax is kept unchanged.

During the time period that the working phase Φ is greater than or equalto the second phase correction threshold Φth3 (such as the time periodT3-Tc), the minimum frequency threshold Fmin is corrected to the minimumcorrection threshold Fmin′, wherein the minimum correction thresholdFmin′ is greater than the minimum frequency threshold Fmin′. Increasingthe minimum frequency threshold can reduce the inductance currentripple, facilitate EMI design and improve efficiency.

During the time period that the working phase Φ is less than the secondphase correction threshold Φth3 (such as the time period T0-T3), theminimum frequency threshold Fmin is kept unchanged.

Further, after the switching frequency range is corrected, the workingmode of the AC-DC conversion circuit may be determined according to themethod provided in any of the foregoing embodiments. For example, duringthe time period T0-T1, the switching frequency F is greater than Fmax′,the actual switching frequency Factual is equal to Fmax′, and the AC-DCconversion circuit may work in the DCM as shown in FIG. 6A, or the AC-DCconversion circuit may work in the CCM as shown in FIG. 6B. During thetime period T3-Tc, the switching frequency F is less than Fmin′, theactual switching frequency Factual is equal to Fmin′, and the AC-DCconversion circuit may work in the CCM. During the time period T1-T3,the switching frequency F is greater than Fmin′ but less than Fmax′, andthe AC-DC conversion circuit may work in the CRM. Further, the controllogic of the circuit in the CRM is determined by comparing the workingphase Φ with the first phase threshold Φth1. For example, during thetime period T1-T2, the working phase t is less than the phase thresholdΦth1, then the AC-DC conversion circuit works in the VOT CRM; during thetime period T2-T3, the working phase t is greater than the first phasethreshold Φth1, then the AC-DC conversion circuit works in the NCR CRM.

The time threshold in the above embodiment may be directly set, or maybe set according to the input current and at least one currentthreshold, or according to the input voltage and at least one voltagethreshold. As shown in FIG. 7 or FIG. 8 , where FIG. 7 is a schematicdiagram of a control method for the AC-DC conversion circuit accordingto a fourth embodiment of the present disclosure, and FIG. 8 is acontrol method for the AC-DC conversion circuit according to a fifthembodiment of the present disclosure.

Referring to FIG. 7 , at least one voltage threshold is set, and thereis no limit to the number and value of the at least one voltagethreshold. For example, the voltage threshold is set as Vth1, Vth2 andVth3, and the time thresholds Tth1, Tth2 and Tth3 are obtained bycomparing the absolute value of the input voltage Vin with the voltagethreshold.

Specifically, at the moment T1, the absolute value of the input voltageVin is equal to the voltage threshold Vth2, and the working timecorresponds to the time threshold Tth2 at this time; at the moment T3,the absolute value of the input voltage Vin is equal to the voltagethreshold Vth3, and the working time corresponds to the time thresholdTth3 at this time; and at the moment T2, the absolute value of the inputvoltage Vin is equal to the voltage threshold Vth1, and the working timecorresponds to the time threshold Tth1 at this time.

Referring to FIG. 8 , at least one current threshold is set, and thereis no limit to the number and value of the at least one currentthreshold. For example, the current threshold is set as Ith1, Ith2 andIth3, and the time thresholds Tth1, Tth2 and Tth3 are obtained bycomparing the absolute value of input current Iin with the currentthreshold.

Specifically, at the moment T1, the absolute value of the input currentIin is equal to the current threshold Ith2, and the working timecorresponds to the time threshold Tth2 at this time; at the moment T3,the absolute value of the input current tin is equal to the currentthreshold Ith3, and the working time corresponds to the time thresholdTth3 at this time; and at the moment T2, the absolute value of the inputcurrent Iin is equal to the current threshold Ith1, and the working timecorresponds to the time threshold Tth1 at this time.

Similarly, the phase threshold in the above embodiment may be directlyset, or may be set according to the input current and at least onecurrent threshold, or according to the input voltage and at least onevoltage threshold. As shown in FIG. 9 or FIG. 10 , where FIG. 9 is aschematic diagram of a control method for the AC-DC conversion circuitaccording to a sixth embodiment of the present disclosure, and FIG. 10is a schematic diagram of a control method for the AC-DC conversioncircuit according to a seventh embodiment of the present disclosure.

Referring to FIG. 9 , at least one voltage threshold is set, and thereis no limit to the number and value of the at least one voltagethreshold. For example, the voltage threshold is set as Vth1, Vth2 andVth3, and the phase thresholds Φth1, Φth2 and Φth3 are obtained bycomparing the absolute value of the input voltage Vin with the voltagethreshold.

Specifically, at the moment T1, the absolute value of the input voltageVin is equal to the voltage threshold Vth2, and the working phasecorresponds to the phase threshold Φth2 at this time; at the moment T3,the absolute value of the input voltage Vin is equal to the voltagethreshold Vth3, and the working phase corresponds to the phase thresholdΦth3 at this time; at the moment T2, the absolute value of the inputvoltage Vin is equal to the voltage threshold Vth1, the working phasecorresponds to the phase threshold Φth1 at this time.

Referring to FIG. 10 , at least one current threshold is set, and thereis no limit to the number and value of the at least one currentthreshold. For example, the current threshold is set as Ith1, Ith2 andIth3, and the phase threshold Φth1, Φth2, Φth3 are obtained by comparingthe absolute value of the input current Iin with the current threshold.

Specifically, at the moment T1, the absolute value of the input currentIin is equal to the current threshold Ith2, and the working phasecorresponds to the phase threshold Φth2 at this time; at the moment T3,the absolute value of the input current tin is equal to the currentthreshold Ith3, and the working phase corresponds to the phase thresholdΦth3 at this time; at the moment T2, the absolute value of the inputcurrent Iin is equal to the current threshold Ith1, and the workingphase corresponds to the phase threshold Φth1 at this time.

Based on the above embodiments, FIG. 11 is a schematic diagram of acontrol method for the AC-DC conversion circuit according to an eighthembodiment of the present disclosure. Taking four voltage correctionthresholds as an example to exemplify the scheme. Referring to FIG. 11 ,the switching frequency range is set as the preset Fmin˜Fmax (as shownby the black dotted line), the switching frequency F is calculated basedon the input voltage, input current, output voltage and output current.Taking the absolute value of the input voltage Vin as a reference, theZVS and a better THD is realized by setting the first voltage thresholdVth1, comparing the absolute value of the input voltage with the firstvoltage threshold Vth1, and selecting the specific control logic of theAC-DC conversion circuit in the CRM. Further, four voltage correctionthresholds Vth2, Vth3, Vth4, Vth5 are set (there is no limit to thenumber and value of voltage correction thresholds in the preset scheme),Fmin and Fmax are corrected through the four voltage correctionthresholds Vth2, Vth3, Vth4, Vth5, and the corrected Fmin1/Fmin2 andFmax1/Fmax2 are shown by the black solid line. Specifically, theabsolute value of the input voltage is compared with the voltagethresholds Vth4 and Vth5 to adjust the Fmax, which can reduce thedriving loss and facilitate the selection of circuit components andmagnetic parts by reducing the maximum frequency threshold; the absolutevalue of the input voltage is compared with the voltage threshold Vth2and Vth3 to adjust the Fmin, which can reduce the current ripple andimprove the efficiency, and facilitate the EMI design.

During the time periods [T0-T1] and [T10-T11], the absolute value of theinput voltage Vin is less than the voltage correction threshold Vth5,and the maximum frequency threshold Fmax during the time periods isadjusted to Fmax1, which is less than the preset Fmax.

During the time periods [T1-T2] and [T9-T10], the absolute value of theinput voltage Vin is greater than the voltage correction threshold Vth5but less than the voltage correction threshold Vth4, and the maximumfrequency threshold Fmax during the time periods is adjusted to Fmax2,which is less than the preset Fmax, where there is no limit to therelationship between Fmax1 and Fmax2.

During the time period [T2-T9], the absolute value of the input voltageVin is greater than the voltage correction threshold Vth4, the maximumfrequency threshold during the time period is kept unchanged, which isthe preset Fmax.

During the time period [T5-T6], the absolute value of the input voltageVin is greater than the voltage correction threshold Vth3, and theminimum frequency threshold Fmin in this time period is adjusted toFmin1, which is greater than the preset Fmin.

During the time periods [T4-T5] and [T6-T7], the absolute value of theinput voltage Vin is greater than the voltage correction threshold Vth2but less than the voltage correction threshold Vth3, and the minimumfrequency threshold Fmin during the time periods is adjusted to Fmin2,which is greater than the preset Fmin, where there is no limit to therelationship between Fmin1 and Fmin2.

During the time periods [T0-T4] and [T7-T11], the absolute value of theinput voltage Vin is less than the voltage correction threshold Vth2,Fmin is changed, so that the minimum frequency threshold in the timeperiod is kept unchanged, which is the preset Fmin.

The input voltage is compared with the voltage correction threshold toobtain the corrected upper frequency limit Fmax1/Fmax2 and the correctedlower frequency limit Fmin1/Fmin2, as shown by the solid black line.Further, the switching frequency F is compared with the correctedswitching frequency range to determine the actual switching frequencyFactual, as shown in FIG. 11 .

During the time periods [T0-T2] and [T9-T11], the switching frequency Fis greater than Fmax2, and the AC-DC conversion circuit works in the DCMor the CCM, the driving loss is reduced by limiting the maximumswitching frequency, and the selection of circuit components andmagnetic parts is facilitated, meanwhile, in the DCM working mode, abetter PF can be obtained by changing the charging time, and in the CCMworking mode, ZVS can be realized, thereby reducing the switching loss.

During the time period [T4-T7], the switching frequency F is less thanFmin2, and the AC-DC conversion circuit works in the CCM, which canreduce the current ripple, improve the efficiency and facilitates theEMI design by selecting different CCM switching frequencies.

During the time periods [T2-T4] and [T7-T9], the switching frequency Fis greater than Fmin2 but less than Fmax2, and the AC-DC conversioncircuit works in the CRM, and the control strategy of the AC-DCconversion circuit under the CRM is selected by comparing the absolutevalue of the input voltage with the first voltage threshold Vth1.Specifically, during the time periods [T2-T3] and [T8-T9], the absolutevalue of the input voltage Vin is less than the first voltage thresholdVth1, and the AC-DC conversion circuit works in the VOT CRM, the THD ofthe input current when the input voltage crossing zero can be improvedby changing the charging time of the inductor. During the time periods[T3-T4] and [T7-T8], the absolute value of the input voltage Vin isgreater than the first voltage threshold Vth1, and the AC-DC conversioncircuit works in the NCR CRM, ZVS can be realized by negative current,so as to reduce the switching loss.

As shown in FIG. 11 , the AC-DC conversion circuit alternates betweenfour working modes, and the actual switching frequency Factual iseffectively limited to a certain range, so that the selection of circuitcomponents and magnetic parts, and EMI design become simple, while theefficiency of the circuit, PF and THD are improved.

Under different input voltages and load conditions, differentcombinations of working modes of the PFC circuit may occur. FIG. 12 is aschematic diagram of a combination of working modes according to anembodiment. As shown in FIG. 12 , under different scenarios or workingconditions, single working mode, dual working mode, triple working modeand quadruple working mode can be realized. Considering that Fmin andFmax can be variable values or fixed value, and the number and value ofthe voltage threshold are not fixed, there are many ways to implementthe scheme. For ease of description, FIGS. 13A to 15 respectively showthe schematic diagrams of the control method in which the circuit worksin the triple working mode, the dual working mode and the single workingmode in a condition that Fmin and Fmax are fixed.

FIGS. 13A-13B are schematic diagrams of a control method for the AC-DCconversion circuit according to a ninth embodiment of the presentdisclosure. As shown in the FIGS. 13A-13B, the switching frequency rangeof the AC-DC conversion circuit is set as Fmin˜Fmax (as shown by blacksolid line), the switching frequency F is calculated according to theinput voltage, the input current, the output voltage and the outputcurrent, and the switching frequency F is compared with Fmin and Fmax todetermine the actual switching frequency Factual. Further, taking theabsolute value of the input voltage Vin as a reference, the firstvoltage threshold Vth1 is set, and the absolute value of the inputvoltage Vin is compared with the first voltage threshold Vth1 to selectthe control method of the circuit under the CRM, so as to realize ZVSand a better THD.

During the time periods [T0-T1] and [T4-T5], the switching frequency Fis greater than Fmax, the actual switching frequency Factual is set toFmax, the AC-DC conversion circuit works in the DCM as shown in FIG.13A, or the AC-DC conversion circuit works in the CCM as shown in FIG.13B. The driving loss is reduced by reducing the maximum frequencythreshold, and the selection of circuit components and magnetic parts isfacilitated, meanwhile, in the DCM working mode, a better PF can beobtained by changing the charging time, and in the CCM working mode, ZVScan be realized to reduce switching loss.

During the time period [T1-T4], the switching frequency F is greaterthan Fmin but less than Fmax, the AC-DC conversion circuit works in theCRM, and the specific control method under the CRM is selected bycomparing the absolute value of the input voltage with the first voltagethreshold Vth1. During the time periods [T1-T2] and [T3-T4], theabsolute value of the input voltage Vin is less than the first voltagethreshold Vth1, and the AC-DC conversion circuit works in the VOT CRM,the THD of the input current when the input voltage crossing zero can beimproved by changing the charging time of the inductor. During the timeperiod [T2-T3], the absolute value Vin of the input voltage is greaterthan the first voltage threshold Vth1, and the AC-DC conversion circuitworks in the NCR CRM, ZVS can be realized by negative current, therebyreducing the switching loss.

As shown in FIGS. 13A-13B, under the conditions of the output voltageand the load, the AC-DC conversion circuit alternates between threeworking modes, and the actual switching frequency Factual is effectivelylimited to a certain range, so that the selection of circuit componentsand magnetic parts, and EMI design become simple, while the efficiencyof the circuit, PF and THD are improved.

FIGS. 14A-14B are schematic diagrams of an AC-DC conversion circuitcontrol method according to a tenth embodiment of the presentdisclosure. In FIGS. 14A-14B, the switching frequency range of the AC-DCconversion circuit is set as Fmin˜Fmax (as shown by black solid line),the switching frequency F is calculated according to the input voltage,the input current, the output voltage and the output current, and theswitching frequency F is compared with Fmin and Fmax to determine theactual switching frequency Factual.

During the time periods [T0-T1] and [T2-T3], the switching frequency Fis greater than Fmax, the actual switching frequency Factual is set toFmax, the AC-DC conversion circuit works in the DCM as shown in FIG.14A, or the AC-DC conversion circuit works in the CCM as shown in FIG.14B. The driving loss is reduced by reducing the maximum frequencythreshold, and the selection of circuit components and magnetic parts isfacilitated, meanwhile, in the DCM working mode, a better PF can beobtained by changing the charging time, and in the CCM working mode, ZVScan be realized to reduce switching loss.

During the time period [T1-T2], the switching frequency F is greaterthan Fmin but less than Fmax, and the AC-DC conversion circuit works inthe NCR CRM during the time period, ZVS can be realized by negativecurrent, thereby reducing the switching loss.

As shown in FIGS. 14A-14B, under the conditions of the output voltageand the output current, the AC-DC conversion circuit alternates betweentwo working modes, and the actual switching frequency Factual iseffectively limited to a certain range, so that the selection of circuitcomponents and magnetic parts, and EMI design become simple, while theefficiency of the circuit, PF and THD are improved.

FIGS. 15A-15B are schematic diagrams of an AC-DC conversion circuitcontrol method according to an eleventh embodiment of the presentdisclosure. In FIGS. 15A-15B, the switching frequency range of thecircuit is set as fixed Fmin Fmax (as shown by the black solid line),and the switching frequency F is calculated based on the input voltage,the output voltage and the load, and the switching frequency F iscompared with Fmin and Fmax to determine the actual switching frequencyFactual.

During the entire time period [T0-T1], the switching frequency F isgreater than Fmax, so that the actual switching frequency Factual is setto Fmax, and the AC-DC conversion circuit works in the DCM during theentire period as shown in FIG. 15A, or the AC-DC conversion circuitworks in the CCM during the entire period as shown in FIG. 15B. Thedriving loss is reduced by reducing the maximum frequency threshold, andthe selection of circuit components and magnetic parts is facilitated,meanwhile, in the DCM working mode, a better PF can be obtained bychanging the charging time, and in the CCM working mode, ZVS can berealized to reduce switching loss.

As shown in FIGS. 15A-15B, under the conditions of the input voltage andthe load, the AC-DC conversion circuit has only one working mode, andthe actual switching frequency Factual is effectively limited to acertain range, so that the selection of circuit components and magneticparts, and EMI design become simple, while the efficiency of thecircuit, PF and THD are improved.

In summary, the bridgeless PFC circuit control method proposed in thepresent disclosure can effectively limit the switching frequency rangeof the PFC circuit, and achieve better THD, PF, efficiency and EMIcharacteristics under different input voltages and full-range loadconditions.

Based on the above embodiment, a control method for the AC-DC conversioncircuit includes: acquiring circuit parameter information of the AC-DCconversion circuit; and limiting an actual switching frequency or anactual switching period of the AC-DC conversion circuit within a presetworking range according to the circuit parameter information, in anentire load range.

In a possible embodiment, the circuit parameter information includes oneor more of the following: an input voltage, an input current, an outputvoltage and an output current.

In a possible embodiment, the present disclosure calculates theswitching frequency or the switching period based on the circuitparameter information of the AC-DC conversion circuit, which is comparedwith the preset working range to obtain the actual switching frequencyor the actual switching period of the AC-DC conversion circuit.

In a condition that the switching frequency reaches an upper limit ofthe preset switching frequency range, the actual switching frequency ofthe AC-DC conversion circuit is controlled to be the upper limit; in acondition that the switching frequency reaches a lower limit of thepreset switching frequency range, the actual switching frequency of theAC-DC conversion circuit is controlled to be the lower limit.

Further, in a condition that the switching frequency exceeds the upperlimit of the preset switching frequency range, the AC-DC conversioncircuit is controlled to work in DCM or CCM; in a condition that theswitching frequency is within the preset switching frequency range, theAC-DC conversion circuit is controlled to work in CRM; in a conditionthat the switching frequency is lower than the lower limit of the presetswitching frequency range, the AC-DC conversion circuit is controlled towork in CCM.

Further, when the AC-DC conversion circuit works in the CRM: a controllogic is determined according to at least one variable of the absolutevalue of the input voltage, the working time and the working phase andthe preset first parameter threshold; in a condition that the variableis less than or equal to the first parameter threshold, the controlcircuit is controlled to work in a VOT CRM, and the charging time of aninductor of the AC-DC conversion circuit is controlled; in a conditionthat the variable is greater than the first parameter threshold, thecontrol circuit is controlled to work in a NCR CRM, and the inductorcurrent is controlled to reach negative value to realize ZVS of powerswitches.

In a possible implementation, the present disclosure sets at least oneparameter correction threshold, and corrects an upper limit of thepreset working range and/or a lower limit of the preset working rangeaccording to at least one variable of the absolute value of the inputvoltage, the working time and the working phase of the AC-DC conversioncircuit, where the parameter correction threshold may be a voltagecorrection threshold, a time correction threshold, a phase correctionthreshold, and the like.

FIG. 16 is a schematic structural diagram of a control apparatus for theAC-DC conversion circuit according to an embodiment of the presentdisclosure. Referring to FIG. 16 , the control apparatus 10 includes: asampling module 11, configured to detect input information and outputinformation of an AC-DC conversion circuit; and a processing module 12,configured to calculate working information of an AC-DC conversioncircuit according to the input information and the output information ofthe AC-DC conversion circuit, wherein the input information includes aninput voltage and an input current, the output information includes anoutput voltage and an output current, and the working informationincludes a switching frequency or a switching period.

And the processing module 12 is further configured to compare theworking information of the AC-DC conversion circuit with a presetworking range to determine an actual working information and workingmode of the AC-DC conversion circuit, which can improve the THD, PF,efficiency and EMI and the like of the AC-DC conversion circuit.

In a possible design, the processing module 12 is configured to comparethe switching frequency of the AC-DC conversion circuit with the presetswitching frequency range to obtain an actual switching frequency of theAC-DC conversion circuit.

In a condition that the switching frequency is greater than or equal toa maximum frequency threshold, the processing module 12 is configured tocontrol the AC-DC conversion circuit to work in DCM or a CCM, andcontrol the actual switching frequency of the AC-DC conversion circuitto be the maximum frequency threshold, wherein the maximum frequencythreshold is an upper limit of the preset switching frequency range.

In a condition that the switching frequency is less than or equal to aminimum frequency threshold, the processing module 12 is configured tocontrol the AC-DC conversion circuit to work in CCM, and control theactual switching frequency of the AC-DC conversion circuit to be theminimum frequency threshold, wherein the minimum frequency threshold isa lower limit of the preset switching frequency range.

In a condition that the switching frequency is less than the maximumfrequency threshold but greater than the minimum frequency threshold,the processing module 12 is configured to control the AC-DC conversioncircuit to work in CRM.

In a possible design, when the AC-DC conversion circuit works in CRM,the processing module 12 is further configured to determine a controllogic according to the absolute value of the input voltage and a firstvoltage threshold. In a condition that the absolute value of the inputvoltage is less than or equal to the first voltage threshold, theprocessing module 12 is configured to control the AC-DC conversioncircuit to work in VOT CRM, and control to change a charging time of aninductor in the AC-DC conversion circuit. In a condition that theabsolute value of the input voltage is greater than the first voltagethreshold, the processing module 12 is configured to control the AC-DCconversion circuit to work in NCR CRM, and control the inductor currentto reach a negative value to realize zero voltage switching ZVS of powerswitches.

On the basis of the above embodiment, FIG. 17 is a schematic structuraldiagram of a control apparatus for the AC-DC conversion circuitaccording to an embodiment of the present disclosure. Referring to FIG.17 , the apparatus 10 further includes a correcting module 13,configured to correct the maximum frequency threshold and the minimumfrequency threshold according to at least one variable of an absolutevalue of the input voltage, a working time, and a working phase of theAC-DC conversion circuit.

In a possible design, the correcting module 13 sets a first voltagecorrection threshold and a second voltage correction threshold. During atime period that the absolute value of the input voltage is less than orequal to the first voltage correction threshold, the correcting module13 corrects the maximum frequency threshold as a maximum correctionthreshold, wherein the maximum correction threshold is less than themaximum frequency threshold. During a time period that the absolutevalue of the input voltage is greater than the first voltage correctionthreshold, the correcting module 13 keeps the maximum frequencythreshold unchanged. During a time period that the absolute value of theinput voltage is greater than or equal to the second voltage correctionthreshold, the correcting module 13 corrects the minimum frequencythreshold as a minimum correction threshold, wherein the minimumcorrection threshold is greater than the minimum frequency threshold.During a time period that the absolute value of the input voltage isless than the second voltage correction threshold, the correcting module13 keeps the minimum frequency threshold unchanged.

In a possible design, the correction module 13 sets a first timecorrection threshold and a second time correction threshold. During atime period that the working time is less than or equal to the firsttime correction threshold, the correction module 13 corrects the maximumfrequency threshold as a maximum correction threshold, wherein themaximum correction threshold is less than the maximum frequencythreshold. During a time period that the working time is greater thanthe first time correction threshold, the correction module 13 keeps themaximum frequency threshold unchanged. During a time period that theworking time is greater than or equal to the second time correctionthreshold, the correction module 13 corrects the minimum frequencythreshold as a minimum correction threshold, wherein the minimumcorrection threshold is greater than the minimum frequency threshold.During a time period that the working time is less than the second timecorrection threshold, keeps the minimum frequency threshold unchanged

In a possible design, the correction module 13 sets a first phasecorrection threshold and a second phase correction threshold. During atime period that the working phase is less than or equal to the firstphase correction threshold, the correction module 13 corrects themaximum frequency threshold as a maximum correction threshold, whereinthe maximum correction threshold is less than the maximum frequencythreshold. During a time period that the working phase is greater thanthe first phase correction threshold, the correction module 13 keeps themaximum frequency threshold unchanged. During a time period that theworking phase is greater than or equal to the second phase correctionthreshold, the correction module 13 corrects the minimum frequencythreshold as a minimum correction threshold, wherein the minimumcorrection threshold is greater than the minimum frequency threshold.During a time period that the working phase is less than the secondphase correction threshold, the correction module 13 keeps the minimumfrequency threshold unchanged.

The control apparatus of the AC-DC conversion circuit provided in theembodiment can execute the technical solutions of the above methodembodiments, and their implementation principles and technical effectsare similar, which will not be repeated hereby.

An embodiment of the present disclosure further provides a terminaldevice, referring to FIG. 18 , the embodiment of the present disclosureis only illustrated by the example of FIG. 18 , which does not mean thatthe scheme is limited thereto.

FIG. 18 is a schematic diagram of a hardware structure of an electronicdevice according to an embodiment of the present disclosure. Referringto FIG. 18 , the electronic device 200 provided in the embodiment mayinclude: a memory 201 and a processor 202. In an embodiment, theelectronic device 200 further includes a bus 203. The bus 203 is used torealize the connection between the components. The memory 201 storescomputer execution instructions; and the processor 202 executes thecomputer execution instructions stored in the memory 201 to executecontrol method for the AC-DC conversion circuit according to theforegoing embodiments in the first device side.

The memory and the processor are directly or indirectly electricallyconnected to realize the control of the AC-DC conversion circuit. Forexample, these components can be electrically connected to each otherthrough one or more communication buses or signal lines. The memorystores computer execution instructions for implementing the data accesscontrol method, including at least one software function module that canbe stored in the memory in the form of software or firmware. Theprocessor executes various functional applications and data processingby running the software programs and modules stored in the memory.

The memory may be, but not limited to, Random Access Memory (RAM), ReadOnly Memory (ROM), Programmable Read-Only Memory (PROM), ErasableProgrammable Read-Only Memory (EPROM), Electric Erasable ProgrammableRead-Only Memory (EEPROM) and etc. The memory is configured to store aprogram, and the processor executes the program after receiving theexecution instruction. Further, the software program and module in theforegoing memory may further include a working system, which may includevarious software components and/or drivers for managing system tasks(e.g., memory management, storage device control, power management,etc.), and it may communicate with various hardware or softwarecomponents to provide a working environment for other softwarecomponents.

The processor may be an integrated circuit chip capable of signalprocessing. The foregoing processor 202 may be a general processingunit, including Central Processing Unit (CPU), Network Processor (NP),and the like. The methods, steps, and logic diagrams disclosed in theembodiments of the scheme may be implemented or executed. The generalprocessing unit may be a microprocessor, or the processor may be anyconventional processor or the like.

An embodiment of the present disclosure further provides acomputer-readable storage medium on which computer executioninstructions are stored. When the computer execution instructions areexecuted by the processor, the AC-DC conversion circuit control methodaccording to any of the foregoing embodiments may be implemented.

The computer-readable storage medium in the embodiment may be anyavailable medium that can be accessed by a computer, or a data storagedevice such as a server or data center that includes one or moreavailable medium integration. The available medium may be a magneticmedium (e.g., Floppy disk, hard disk, magnetic tape), an optical medium(e.g., DVD), or a semiconductor medium (e.g., SSD), etc.

A person skilled in the art may understand that all or part of the stepsfor implementing the method of the foregoing embodiments may becompleted by hardware relevant to program instructions. Theaforementioned program may be stored in a computer-readable storagemedium. When the program is executed, the steps of the foregoing methodembodiments are executed; the foregoing storage medium includes variousmedium that can store program codes, such as a hard disk, ROM, RAM,magnetic disk, or optical disk.

Finally, it should be noted that the above embodiments are only used toillustrate the technical solutions of the scheme, rather than intendingto limited thereto; although the scheme has been described in detailwith reference to the foregoing embodiments, a person skilled in the artshould understand that: the technical solutions described in theforegoing embodiments can still be modified, or some or all of thetechnical features therein can be equivalently replaced; and thesemodifications or variations do not deviate the essence of thecorresponding technical solutions from the scope of the technicalsolutions of the embodiments in the present disclosure.

What is claimed is:
 1. A control method for an AC-DC conversion circuit,comprising: acquiring circuit parameter information of the AC-DCconversion circuit, wherein the circuit parameter information comprisesone or more of the following: an input voltage, an input current, anoutput voltage and an output current of the AC-DC conversion circuit;limiting an actual switching frequency or an actual switching period ofthe AC-DC conversion circuit within a preset working range according tothe circuit parameter information, in an entire load range; in acondition that a calculated switching frequency is greater than or equalto an upper limit of a preset switching frequency range, controlling theactual switching frequency of the AC-DC conversion circuit to be theupper limit of the preset switching frequency range; in a condition thatthe calculated switching frequency is less than or equal to a lowerlimit of the preset switching frequency range, controlling the actualswitching frequency of the AC-DC conversion circuit to be the lowerlimit of the preset switching frequency range; in a condition that thecalculated switching frequency is greater than or equal to the upperlimit of the preset switching frequency range, controlling the AC-DCconversion circuit to work in a discontinuous conduction mode (DCM) or acontinuous conduction mode (CCM) or a variable on-time criticalconduction mode (VOT CRM); in a condition that the calculated switchingfrequency is within the preset switching frequency range, controllingthe AC-DC conversion circuit to work in a critical conduction mode(CRM); and in a condition that the calculated switching frequency isless than or equal to the lower limit of the preset switching frequencyrange, controlling the AC-DC conversion circuit to work in the CCM; whenthe AC-DC conversion circuit is in the CRM, the method furthercomprising: comparing at least one variable of an absolute value of theinput voltage, a working time and a working phase with a first parameterthreshold; in a condition that the at least one variable is less than orequal to the first parameter threshold, controlling the AC-DC conversioncircuit to work in the VOT CRM, and controlling the AC-DC conversioncircuit to change a charging time of an inductor in the AC-DC conversioncircuit; and in a condition that the at least one variable is greaterthan the first parameter threshold, controlling the AC-DC conversioncircuit to work in a negative current critical conduction mode (NCRCRM), and controlling an inductor current to reach a negative value torealize zero voltage switching (ZVS) of a switch of the AC-DC conversioncircuit.